In a piston pump of this type manufactured by J. Wagner GmbH, Markdorf, Germany, under the designation HC 12000G, there is an inlet valve upline from the differential piston having a ball as its valve gate, which is opened during a suction motion of the differential piston, so that the medium to be processed is drawn into the first pressure chamber. At the same time, the medium located in the second pressure chamber is fed to the implement, and the second pressure chamber is filled again by medium flowing from the first pressure chamber. Thus continuous transport is provided during both displacement motions of the differential piston.
Although operating pressures up to 230 bar can be produced with this piston pump, the inlet valve sometimes does not close the first pressure chamber reliably during a displacement motion in the direction of the inlet valve, so that medium is pushed back into the storage reservoir. But it is particularly disadvantageous that when viscous media are processed, the first pressure chamber is often not completely filled during an intake stroke. As a result, the flow to the implement is not constant, and brief interruptions occur, so that the delivery flow may possibly break off and/or layers of varying thickness may be applied. Air pockets may also form in the medium, which have an undesirable effect on the processing of the medium.